A method and apparatus for generating a color-sequential LCD image display through controlling pixelized display elements for rendering a plurality of colors in sequence, whilst combining control signals for two successive colors against impurities from non-instantaneous response.
The invention relates to a color sequential display apparatus. Color sequential imaging systems generally use a single element to create red, blue, green and possibly white images sequentially in time for a particular pixel, although other color combinations have been used as well. If this image element, or the controlling mechanism in general has relaxation effects, the various color images may influence each other. In principle, an electronic pre-correction system may mitigate such effects, but this would require either introducing an additional image memory, or rather a higher bandwidth.
In consequence, amongst other things, it is an object of the present invention to effect such compensation at least in part, without needing additional expensive hardware. The inventor has recognized that in principle, the various colors are provided in parallel at a certain stage of the image generating.
Now therefore, according to one of its aspects the invention is characterized by executing a compensating operation against color impurities for a later color due to a non-instantaneous response of a display element as a result of an immediately preceding color for the element, under control of the combined color signals associated with both the immediately preceding color and the later color. Generally, color sequential systems have lower system costs compared to systems wherein for each separate color a particular pixel would need a specific image element to be used in parallel for creating a color image. However, the most popular element in use today, to wit LCD, is relatively slow in reacting to control signals applied thereto. In a color-sequential application, such relaxation means that information displayed in a first color may xe2x80x9cbleedxe2x80x9d into another next-following color for the same pixel. If, for example, the sequence is read-green-blue-red-etcetera, information contained in the green image may be influenced by the immediately preceding red image. The effect can be mitigated by electrically pre-correcting the signal fed to the image element. However, to do this, the pre-correction system must access the immediately preceding multicolor image. Converting a standard RGB image into a color sequential signal requires an image memory. Subsequent accessing of this information for color correction would then necessitate to double the bandwidth of the image memory, with associated cost increase. In contradistinction, according to the present invention the pre-correction is executed at an instant before converting from RGB to a color-sequential signal. At such earlier instant, the various color control signals would be available simultaneously. The optimum solution for an RGB sequence has the pre-correction of the green based on the red signal, and the pre-correction of the blue signal based on the red signal. Basing the pre-correction of the red signal on the blue signal from the previous frame would again require an image memory for one color, because this blue color image was then the most recent image sent to the image element.
If also applying the correction mechanism to the first color control signal for the current image, the usage of an additional image memory is obviated by not using the blue signal of the previous frame, but rather the blue signal of the current frame or image. For static images, the correction mechanism will now be perfect. For non-stationary images however, some motion-induced color artefacts may occur. These small effects would introduce some bleeding of one color into another color. The worst case occurs when a saturated blue object moves over an almost black area. The pre-correction will now give a result that is slightly mislocated. Certain user tests have however found that the resultant effect is generally overlooked, inter alia, because the human eye/brain combination tends to be less sensitive for many temporal changes.
The invention also relates to an apparatus being arranged for practicing a method characterized by executing a compensating operation against color impurities for a later color due to a non-instantaneous response of a display element as a result of an immediately preceding color for the element, under control of the combined color signals associated with both the immediately preceding color and the later color.